The prior art is replete with scores of patents which describe image acquisition systems. Such systems are useful for acquiring and producing images of a variety of objects for varied applications.
In these systems, various types of electromagnetic radiation are used to illuminate or interrogate an object. One type of image acquisition system utilizes electronic circuitry to obtain, process, and produce an image of an object or article.
In these electronic systems, an image sensor is often utilized to receive reflected or refracted electromagnetic radiation from the object. Alternatively, the image sensor may receive transmitted electromagnetic radiation that has passed through the object.
Often, the image sensor is connected to a controller which is configured to receive signals produced by the image sensor and to provide control signals which control the rate of image acquisition and signal transfer.
Some types of objects or articles are difficult to interrogate by image acquisition systems when the electromagnetic radiation is received by the image sensor having passed through the object or article. When the electromagnetic radiation travels along a path through the object or article under interrogation, the resulting electromagnetic radiation that exits the object and is received by the image sensor is often a function of the density of the object along the path of travel of the electromagnetic radiation.
An especially challenging object or article for interrogation is a cylindrical container such as a bottle, can, or jar. In this situation, the path length of the electromagnetic radiation through the object or material varies significantly depending on the spatial position of the container relative to the beam of electromagnetic radiation. For example, in bottles containing low density fluid, the density along a path of travel through an edge of the container can be significantly greater than the density encountered along a path of travel through a mid region of the bottle because the density of the container walls can significantly attenuate the electromagnetic radiation. Alternatively, in a thin walled container containing a dense fluid, the density along the path of travel through a mid region of the bottle can be significantly greater than the density encountered along the path of travel through an edge of the container.
These various density paths present challenges to the image sensor due to the finite dynamic range of the sensor. The relative merit of the interrogation of the image acquisition system begins to degrade as the difference in the density paths approaches the dynamic range of the sensor. The relative merit or performance of the image acquisition system becomes especially poor when the difference in path density exceeds the dynamic range of the sensor.
This degradation of relative merit or performance decreases the effectiveness of the interrogation of the object or article, effectively blocking or blinding certain portions of the object or article.
In the production of food articles, desired comestible products are introduced into containers such as bottles or cans for preservation and delivery to a consumer. Occasionally, undesirable foreign objects are also introduced into the containers during the process of manufacture. These undesirable foreign objects have the potential of producing discomfort or harm to the consumer. For this reason, image acquisition systems employing electromagnetic radiation to travel along a plurality of paths through the container to effectively interrogate the object are employed by manufacturers to identify containers containing undesirable foreign objects before they reach the consumer. Often, x-ray radiation is chosen in these applications as the form of electromagnetic radiation due to its superior characteristics. An exemplary example of such an image acquisition system is illustrated and discussed in the U.S. Pat. No. 6,872,001 and incorporated herein.
The merit or effectiveness of the interrogation is especially important in this example since this has a direct bearing on the overall percentage or ratio of containers having foreign material that are caught or intercepted before reaching the consumer. Unfortunately, the characteristics of the containers or objects themselves can vary significantly from object to object and lot to lot which can confound the interrogation process resulting in erroneous information. This erroneous information can cause loss of productivity in the case of false rejections or loss of quality in the case of false acceptance.
So, what is needed is an apparatus and method for acquiring an image of an object to effectively inspect an object that is not prone or vulnerable to substantial blocking or blinding of certain portions of the object due to variations in the density of the path of travel of the electromagnetic radiation through the object.